Ultraviolet Device Encapsulant

ABSTRACT

A composite material, which can be used as an encapsulant for an ultraviolet device, is provided. The composite material includes a matrix material and at least one filler material incorporated in the matrix material that are both at least partially transparent to ultraviolet radiation of a target wavelength. The filler material includes microparticles and/or nanoparticles and can have a thermal coefficient of expansion significantly smaller than a thermal coefficient of expansion of the matrix material for relevant atmospheric conditions. The relevant atmospheric conditions can include a temperature and a pressure present during each of: a curing and a cool down process for fabrication of a device package including the composite material and normal operation of the ultraviolet device within the device package.

REFERENCE TO RELATED APPLICATIONS

The present patent application is a continuation-in-part of U.S.application Ser. No. 13/624,162, titled “Ultraviolet DeviceEncapsulant,” filed on 21 Sep. 2012, which claims the benefit of U.S.Provisional Application No. 61/538,115, titled “Ultraviolet LightEmitting Diode Encapsulant,” filed on 22 Sep. 2011, each of which ishereby incorporated by reference in its entirety to provide continuityof disclosure.

GOVERNMENT LICENSE RIGHTS

This invention was made with Federal government support under ContractNo. W911NF-10-2-0023 awarded by Defense Advanced Research ProjectsAgency (DARPA). The government has certain rights in the invention.

TECHNICAL FIELD

The disclosure relates generally to ultraviolet light emitting devices,and more particularly, to an encapsulant for ultraviolet light emittingdevices.

BACKGROUND ART

With recent advances in group III-based ultraviolet (UV) light emittingdiode (LED) technology, interest in using UV LEDs for variousapplications, such as disinfection of medical tools, water purification,fluorescence spectroscopy, medical therapy, and the like, is increasing.Despite tremendous efforts, UV LEDs continue to suffer from relativelylow external quantum efficiencies. Improvement in light extraction fromthe UV LED structure can increase the overall efficiency of a device.One approach for improving light extraction uses an index matchingencapsulant (e.g., similar to the approach used for visible LEDs) inorder to decrease the total internal reflection (TIR) from the devicesurfaces and, as a result, extract more light from the UV LED.

Typical epoxy resin materials used for visible LED encapsulation are notadequate for UV LEDs as the resins are not sufficiently transparent toUV radiation and quickly deteriorate under the UV radiation. An idealencapsulant should be “stable.” In particular, the optical and physicalproperties of the encapsulant should not change during packaging, LEDassembly, and during the operating lifetime of the LED. For example, anencapsulant should be resistant to heating during the LED assembly, suchas during soldering a chip onto a printed circuit board or during acuring process. During the curing process, drying of the encapsulant canfurther induce stresses in the material. As a result, an encapsulantthat is not prone to crack during the curing procedure can be selected.

A thermal coefficient of expansion (TCE) of the encapsulant can bechosen to match the TCE of an LED package in order to reduce stressesduring temperature cycling, which can occur during the manufacture andoperation of the LED. One approach to control TCE is by designing acomposite material having the desired thermal characteristics. Forexample, epoxy-based optically transparent nano-composites have beenstudied for photonic packaging, and the effect the particle fraction ofa silica filler has on the thermal coefficient of expansion of thecomposite material has been analyzed. TCE also has been investigatedwith respect to the effect of percolation in a silicon carbide (SiC)whisker reinforced ceramic composite. The effects of silica filler onthe mechanical properties of a composite encapsulant have also beeninvestigated.

SUMMARY OF THE INVENTION

This Summary Of The Invention introduces a selection of certain conceptsin a brief form that are further described below in the DetailedDescription Of The Invention. It is not intended to exclusively identifykey features or essential features of the claimed subject matter setforth in the Claims, nor is it intended as an aid in determining thescope of the claimed subject matter.

Aspects of the invention provide a composite material, which can be usedas an encapsulant for an ultraviolet device. The composite materialincludes a matrix material and at least one filler material incorporatedin the matrix material that are both at least partially transparent toultraviolet radiation of a target wavelength. The filler materialincludes microparticles and/or nanoparticles and can have a thermalcoefficient of expansion significantly smaller than a thermalcoefficient of expansion of the matrix material for relevant atmosphericconditions. The relevant atmospheric conditions can include atemperature and a pressure present during each of: a curing and a cooldown process for fabrication of a device package including the compositematerial and normal operation of the ultraviolet device within thedevice package.

A first aspect of the invention provides a composite materialcomprising: a matrix material at least partially transparent toultraviolet radiation of a target wavelength and having a matrixmaterial thermal coefficient of expansion; and at least one fillermaterial at least partially transparent to the ultraviolet radiationincorporated in the matrix material, wherein the at least one fillermaterial includes at least one of: microparticles or nanoparticles.

A second aspect of the invention provides a device package comprising:an ultraviolet device; and an encapsulant located adjacent to at leastone surface of the ultraviolet device, wherein the encapsulant is acomposite material including: a matrix material at least partiallytransparent to ultraviolet radiation of a target wavelength and having amatrix material thermal coefficient of expansion; and at least onefiller material at least partially transparent to the ultravioletradiation incorporated in the matrix material, wherein the at least onefiller material includes at least one of: microparticles ornanoparticles.

A third aspect of the invention provides a device package comprising: anultraviolet device; and an encapsulant located adjacent to at least onesurface of the ultraviolet device, wherein the encapsulant is acomposite material including: a matrix material at least partiallytransparent to ultraviolet radiation of a target wavelength and having amatrix material thermal coefficient of expansion; a first fillermaterial at least partially transparent to the ultraviolet radiationincorporated in the matrix material, wherein the first filler materialincludes at least one of: microparticles or nanoparticles and has afiller thermal coefficient of expansion significantly smaller than thematrix material thermal coefficient of expansion for relevantatmospheric conditions; and a second filler material including aplurality of fluorescent particles incorporated in the matrix material,wherein the plurality of fluorescent particles are visibly fluorescentunder exposure to the ultraviolet radiation.

A fourth aspect of the invention provides a device package, comprising:an ultraviolet device for which operation involves ultraviolet radiationof a target wavelength; and an encapsulant located adjacent to at leastone surface of the ultraviolet device, wherein the encapsulant is acomposite material including: a matrix material at least partiallytransparent to ultraviolet radiation of the target wavelength and havinga matrix material thermal coefficient of expansion; and at least onefiller material at least partially transparent to the ultravioletradiation incorporated in the matrix material, wherein the at least onefiller material includes a combination of microparticles andnanoparticles and has a filler thermal coefficient of expansion at leastthree times smaller than the matrix material thermal coefficient ofexpansion for atmospheric conditions present during a curing and a cooldown process for fabrication of the device package, and wherein aconcentration of the at least one filler material in the compositematerial exceeds a percolation threshold for the filler material.

A fifth aspect of the invention provides a device package, comprising:an ultraviolet device for which operation involves ultraviolet radiationof a target wavelength; an encapsulant located adjacent to at least onesurface of the ultraviolet device, wherein the encapsulant comprises aplurality of layers, with at least one of the layers formed of acomposite material including: a matrix material at least partiallytransparent to ultraviolet radiation of the target wavelength and havinga matrix material thermal coefficient of expansion; and a fillermaterial at least partially transparent to the ultraviolet radiationincorporated in the matrix material and having a filler material thermalcoefficient of expansion at least three times smaller than the matrixmaterial thermal coefficient of expansion for relevant atmosphericconditions present during a curing and a cool down process forfabrication of the device package, wherein the filler material includesa combination of microparticles and nanoparticles; and a transitionlayer separating at least two of the plurality of layers of theencapsulant, wherein the transition layer includes a bonding layer.

A sixth aspect of the invention provides a device package, comprising:an ultraviolet device for which operation involves ultraviolet radiationof a target wavelength; and an encapsulant located adjacent to at leastone surface of the ultraviolet device, wherein the encapsulant comprisesa composite material having a plurality of composite domains shaped toform an optical element located about an emitting surface of theultraviolet device, each composite domain having a distinct compositionof a matrix material at least partially transparent to ultravioletradiation of the target wavelength and having a matrix material thermalcoefficient of expansion.

The illustrative aspects of the invention are designed to solve one ormore of the problems herein described and/or one or more other problemsnot discussed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the disclosure will be more readilyunderstood from the following detailed description of the variousaspects of the invention taken in conjunction with the accompanyingdrawings that depict various aspects of the invention.

FIGS. 1A-1B show schematics of illustrative ultraviolet device packagesaccording to embodiments.

FIGS. 2A-2D show illustrative encapsulants including spherical fillermaterial according to embodiments.

FIG. 3 shows an illustrative encapsulant including elongate fillermaterial according to an embodiment.

FIG. 4 shows an illustrative encapsulant having a radially non-uniformdistribution of the filler material according to an embodiment.

FIG. 5 shows an illustrative encapsulant including a plurality of layersaccording to an embodiment.

FIG. 6 shows another illustrative encapsulant including a plurality oflayers according to an embodiment.

FIGS. 7A and 7B show illustrative encapsulants including multiple typesof filler material according to embodiments.

FIG. 8 shows an illustrative encapsulant having a layered structureaccording to an embodiment.

FIG. 9 shows an illustrative device including an anti-reflective coatingaccording to an embodiment.

FIGS. 10A-10C show illustrative encapsulants having multiple segments ofdisjointed domains each forming an optical element according toembodiments.

FIG. 11 shows an illustrative ultraviolet device package having anencapsulant with multiple segments of disjointed domains that form anoptical element according to an embodiment.

FIG. 12 shows an illustrative flow diagram for fabricating a circuitaccording to an embodiment.

It is noted that the drawings may not be to scale. The drawings areintended to depict only typical aspects of the invention, and thereforeshould not be considered as limiting the scope of the invention. In thedrawings, like numbering represents like elements between the drawings.

DETAILED DESCRIPTION OF THE INVENTION

As indicated above, aspects of the invention provide a compositematerial, which can be used as an encapsulant for an ultraviolet device.The composite material includes a matrix material and at least onefiller material incorporated in the matrix material that are both atleast partially transparent to ultraviolet radiation of a targetwavelength. The filler material includes microparticles and/ornanoparticles and can have a thermal coefficient of expansionsignificantly smaller than a thermal coefficient of expansion of thematrix material for relevant atmospheric conditions. The relevantatmospheric conditions can include a temperature and a pressure presentduring each of: a curing and a cool down process for fabrication of adevice package including the composite material and normal operation ofthe ultraviolet device within the device package.

As used herein, a material is at least partially transparent when thematerial allows at least a portion of electromagnetic radiation in acorresponding a target radiation wavelength to pass there through. Forexample, a layer can be configured to be at least partially transparentto a target wavelength corresponding to a range of radiation wavelengthsdefined by a peak emission wavelength for an ultraviolet device +/− fivenanometers. As used herein, a layer is at least partially transparent toradiation if it allows more than approximately 0.5 percent of theradiation to pass there through. In a more particular embodiment, an atleast partially transparent layer is configured to allow more thanapproximately five percent of the radiation to pass there through. In astill more particular embodiment, an at least partially transparentlayer is configured to allow more than approximately ten percent of theradiation to pass there through. Furthermore, as used herein, unlessotherwise noted, the term “set” means one or more (i.e., at least one)and the phrase “any solution” means any now known or later developedsolution.

Turning to the drawings, FIGS. 1A and 1B show schematics of illustrativeultraviolet device packages 10A, 10B, respectively, according toembodiments. In FIG. 1A, the device package 10A includes an ultravioletdevice 12 located within an enclosure 14, both of which are located on aheat sink 16. In FIG. 1B, the device package 10B includes an ultravioletdevice 12 located on a submount 18, both of which are located within theenclosure 14. However, it is understood that these configurations areonly illustrative of various configurations for device packages 10A,10B.

Regardless, the ultraviolet device 12 can comprise any type of unitarydevice or circuit, the operation of which involves ultravioletradiation. For example, the ultraviolet device 12 can comprise any typeof device which when operated, generates, manipulates, detects, iseffected by, and/or the like, ultraviolet radiation having a targetwavelength. Illustrative ultraviolet devices 12 include, for example, anultraviolet light emitting diode (LED), an ultraviolet laser, anultraviolet photodetector, an ultraviolet photodiode, an ultravioletphototransistor, an avalanche ultraviolet photodiode, an ultravioletphotomultiplier, and/or the like. Furthermore, an ultraviolet device 12can comprise a circuit, such as an integrated circuit implemented on achip, a die, and/or the like, which includes one or more unitaryultraviolet devices as circuit components. The target wavelength of theultraviolet radiation can comprise the entire ultraviolet radiationspectrum or any subset of the ultraviolet radiation spectrum. In anembodiment, the target wavelength of the ultraviolet radiation is in arange of wavelengths between approximately 260 nanometers andapproximately 360 nanometers.

The enclosure 14 can comprise any type of enclosure. For example, theenclosure 14 can be configured to provide a protective covering for theultraviolet device 12. Furthermore, the enclosure 14 can be configuredto direct ultraviolet radiation onto and/or away from the ultravioletdevice 12. To this extent, as illustrated, the enclosure 14 can have aconical shape. Furthermore, the enclosure 14 can have an interiorsurface that is at least partially reflective of ultraviolet radiationhaving a target wavelength. In an embodiment, the enclosure 14 is formedof a material having a low absorption coefficient, such that a productof the absorption coefficient and the largest dimension of the enclosure14 is significantly smaller than unity. Furthermore, an index ofrefraction of the enclosure 14 material can be smaller than an index ofrefraction of sapphire. For example, an index of refraction of theenclosure can be approximately equal to a square root of the index ofrefraction of sapphire. The heat sink 16 and submount 18 each cancomprise any type of suitable material. For example, the heat sink 16can be formed of a material having a high thermal conductivity, such asmetal, while the submount 18 can be formed of a material which providesheat spreading, such as silicon carbide, diamond, or the like.

Each device package 10A, 10B further includes an encapsulant 20, whichis at least partially transparent to ultraviolet radiation having atarget wavelength. As illustrated, the encapsulant 20 can fillsubstantially all of the area formed by the enclosure 14. Furthermore,as illustrated in the device package 10B, the encapsulant 20 can enclosethe entire ultraviolet device 12. However, it is understood that theencapsulant 20 can enclose only a portion of the ultraviolet device 12.For example, the encapsulant 20 can be located on a surface of theultraviolet device 12, such as an emitting face or underfill of theultraviolet device 12, through which ultraviolet radiation of the targetwavelength is intended to pass (into or out of the ultraviolet device12) during operation of the ultraviolet device 12. Additionally, theencapsulant 20 can have a curved outer surface 22, which can act as alens for the ultraviolet radiation.

The encapsulant 20 comprises a composite material. In an embodiment, thecomposite material includes a matrix material and at least one fillermaterial incorporated in the matrix material. The at least one fillermaterial can be multiple particles, which can act as a skeleton for theencapsulant 20. The matrix material and/or filler material(s) can beselected and/or configured to provide one or more target attributes forthe encapsulant 20. For example, the matrix and/or filler material(s) ofthe encapsulant 20 can be index-matched ultraviolet transparentmaterials, which can provide improved ultraviolet radiation extractionfrom or passage to the ultraviolet device 12. Furthermore, the matrixand/or filler material(s) of the encapsulant 20 can provide an adhesive(e.g., gluing) agent for the device packages 10A, 10B that is thermallyand mechanically stable, thereby improving an operating lifetime for theultraviolet device 12. The matrix and/or filler materials also can beselected and/or configured to improve thermal management of theultraviolet device 12 during its operation. Additionally, the matrixand/or filler material(s) of the encapsulant 20 can have a thermalcoefficient of expansion that is admissible for the fabrication of thedevice packages 10A, 10B as well as subsequent operation of theultraviolet device 12 within the device package 10A, 10B.

The encapsulant 20 also can be configured to adjust one or moreproperties of the ultraviolet radiation passing through the encapsulant20. To this extent, the filler material(s) can be selected and/orlocated within the matrix material to, for example, control an angulardistribution of emitted ultraviolet radiation, control diffusivescattering, control an index of refraction, and/or the like. The matrixand/or filler materials also can provide an encapsulant 20 in which bothdiffusive scattering and refractive index change abruptly and/orsmoothly throughout the encapsulant 20. In an embodiment, theencapsulant 20 can include filler material particles for subsequentlight conversion. In a further embodiment, the filler material particlesare formed of a material having a low absorption coefficient, such thata product of the absorption coefficient and the largest dimension of thefiller material particles is significantly smaller than unity.Additionally, the encapsulant 20 can be configured to serve as anindicator of ultraviolet operational conditions of the ultravioletdevice 12. For example, the matrix and/or filler materials can include afluorescent material, which is fluorescent in the visible range underexposure to ultraviolet radiation.

The filler material(s) can be selected to adjust one or more electricaland/or mechanical properties for the encapsulant 20 so that theencapsulant 20 is suitable for various requirements including, forexample, fabrication of the device packages 10A, 10B, operation of theultraviolet device 12 within the device package 10A, 10B, and/or thelike. For example, the filler material(s) can be selected to: reduce(e.g., minimize) thermal expansion of the encapsulant 20; increase(e.g., maximize) ultraviolet transparent properties of the encapsulant20; control an effective refractive index of the encapsulant 20; and/orthe like. The encapsulant 20 can include any concentration of the fillermaterial(s). In an embodiment, a concentration of a filler material inthe volume of the encapsulant 20 is greater than or equal to apercolation threshold.

In an embodiment, both the matrix material and the filler material(s)are at least partially transparent to ultraviolet radiation of a targetwavelength for the ultraviolet device 12. Additionally, a refractiveindex of the matrix material can closely match a refractive index of oneor more of the filler material(s). For example, a difference in therefractive indexes of the matrix material and at least one fillermaterial can be less than or equal to approximately ten percent of thehigher refractive index. However, the materials can have thermalcoefficients of expansion that differ substantially in relevantatmospheric conditions (e.g., temperature, pressure, and/or the like).For example, the relevant atmospheric conditions can include atmosphericconditions present during a curing and/or a cool down process forfabrication of a device package 10A, 10B, during normal operation of theultraviolet device 12, and/or the like. In an embodiment, a thermalcoefficient of expansion for the filler material is significantlysmaller (i.e., at least approximately three to seven (e.g., five) timessmaller) than a thermal coefficient of expansion for the matrix materialfor the relevant atmospheric conditions. In a more particularembodiment, a thermal coefficient of expansion for the filler materialis at least an order of magnitude smaller than a thermal coefficient ofexpansion for the matrix material for the relevant atmosphericconditions.

The various matrix materials and filler materials described herein cancomprise any type of suitable materials. In an embodiment, the matrixmaterial comprises a bonding material that is at least partiallytransparent to ultraviolet radiation having a target wavelength (e.g.,between 260 and 360 nanometers). In a more particular embodiment, thematrix material of a thickness of approximately one millimeter has atransparency of at least approximately eighty percent for ultravioletradiation having a wavelength in a range between approximately 260nanometers and approximately 360 nanometers. Illustrative at leastpartially ultraviolet transparent bonding materials for the matrixmaterial include a sol-gel, silicone, an amorphous fluoropolymer, anepoxy, and/or the like. Illustrative at least partially ultraviolettransparent materials for the filler materials include nanoparticlesand/or microparticles formed of alumina sol-gel glass, alumina aerogel,sapphire, aluminum nitride (e.g., single crystal aluminum nitride),boron nitride (e.g., single crystal boron nitride), fused silica, and/orthe like.

FIGS. 2A-2D show illustrative encapsulants 20A-20D, respectively,according to embodiments. Each encapsulant 20A-20D is a compositematerial including a matrix material 24 and at least one filler material26. The filler material 26 can be composed of large and/or small (e.g.,as compared to the size of the ultraviolet device 12) domains. Anillustrative large domain can be, for example, a lens mounted onto thedevice package 10A, 10B (FIGS. 1A, 1B). Regardless, the matrix materialcan act as a glue between two or more filler material 26 domains. Eachfiller material 26 comprises a set of particles. The particles caninclude microparticles (e.g., between approximately 0.1 andapproximately 100 microns in size) and/or nanoparticles (e.g., betweenapproximately 1 and approximately 100 nanometers in size). In anembodiment, the particles are spheres (e.g., microspheres and/ornanospheres). However, it is understood that the filler material 26 caninclude particles of any shape and/or size. In an embodiment, a fillermaterial 26 comprises filler particles having sizes smaller than atarget wavelength of the ultraviolet radiation passing through thecorresponding encapsulant 20A-20D (e.g., a wavelength of the ultravioletradiation emitted by the ultraviolet device 12).

In FIG. 2A, the encapsulant 20A includes filler material 26 composed ofa plurality of particles (e.g., microspheres), each of which forms alarge domain of the filler material 26. Furthermore, the particles ofthe filler material 26 are held in place by the matrix material 24,which can act as a glue. In FIG. 2B, the encapsulant 20B includesmultiple filler materials 26A, 26B. In this case, a first fillermaterial 26A can comprise microparticles, which can form large domains,while a second filler material 26B can comprise a plurality ofnanoparticles (e.g., nanospheres), which can form much smaller domains.In an embodiment, the matrix material 24 itself comprises a compositematerial. In particular, the matrix material 24 can include the secondfiller material 26B embedded within a bonding (glue) material 25, whichcan act as a glue for both filler materials 26A, 26B. However, it isunderstood that the matrix material 24 also can include the bondingmaterial 25, without a filler material 26B, which can be incorporatedinto the matrix material 24 along with the first filler material 26A.

It is understood that the filler materials 26A, 26B can be the same ordifferent types of material. For example, the filler material 26B, whichcan be part of the matrix material 24, can be fluorescent particles. Thefiller material 26B can be selected to identify a wavelength of theradiation emitted by the ultraviolet device 12, e.g., by having one ormore visibly different attributes (e.g., a change in color) based on thewavelength of the ultraviolet radiation. In this case, the fillermaterial 26B can comprise, for example, phosphors (e.g., such as thoseused in white light emitting diodes), semiconductor quantum dot having aband gap smaller than the radiation emitted by the ultraviolet device 12(e.g., in visible wavelengths), and/or the like.

In an embodiment, the encapsulant 20B includes a volume concentration ofthe filler materials 26A, 26B, which exceeds a percolation threshold forthe filler materials 26A, 26B. As the filler materials 26A, 26B may havedifferent percolation thresholds, the concentrations of thecorresponding filler materials 26A, 26B may be different for fillermaterials 26A, 26B within the encapsulant 20B and the bonding material25. For example, the encapsulant 20B can have a concentration ofparticles of one or both filler materials 26A, 26B exceeding a threedimensional percolation threshold, while the bonding material 25 caninclude a concentration of particles that is equal to or exceeds a twodimensional percolation threshold.

FIG. 2C illustrates an embodiment of the encapsulant 20C in which thefiller material 26 comprises a plurality of nanoparticles, which can bedistributed non-uniformly throughout the matrix material 24. Thenon-uniformity of the filler material 26 can form an encapsulant 20Chaving a concentration gradient for the filler material 26, in whichdifferent regions of the encapsulant 20C have different concentrationsof the filler material 26. In this case, the varied concentration of thefiller material 26 can be configured to produce a graded refractiveindex for the encapsulant 20C. The grading can result in a refractiveindex changing smoothly from a refractive index of the matrix material24 to a refractive index of either ambient or the materials of theultraviolet device 12 encapsulated by the encapsulant 20C.

FIG. 2D illustrates an embodiment of the encapsulant 20D including amatrix material 24 and two types of the filler material 26A, 26B. Inthis case, a first type of the filler material 26A is shown comprising asingle large domain that is centrally located with respect to theultraviolet device 12, while the second type of the filler material 26Bis shown having a distribution within the composite material 20D thatvaries with respect to a distance from a surface of the ultravioletdevice 12 to an external surface of the encapsulant 20D. In anembodiment, a spatial distribution of the filler material 26B can beconfigured to provide wave guiding for the ultraviolet radiation passingthrough the encapsulant 20D. For example, the spatial distribution ofthe filler material 26B can be radially symmetric.

As discussed herein, it is understood that the filler material 26 cancomprise a set of particles of any shape. To this extent, FIG. 3 showsan illustrative encapsulant 20E including elongate particles of fillermaterial 26C according to an embodiment. In this case, the fillermaterial 26C comprises a plurality of particles (e.g., whiskers), eachof which has a high aspect ratio (e.g., ten to one or greater).Furthermore, the filler material 26C can have a thermal coefficient ofexpansion that is significantly lower than that of the matrix material24. As illustrated, the filler material 26C can be distributed in arandom manner, e.g., with varying concentrations, orientations, and/orthe like, throughout the encapsulant 20E.

FIG. 4 shows an illustrative encapsulant 20F having a radiallynon-uniform distribution of the filler material 26 according to anembodiment. As illustrated, the filler material 26 can be configured toprovide a plurality of paths from the ultraviolet device 12 to anexternal surface of the encapsulant 20F. The plurality of paths can beused, for example, to control thermal and/or optical properties of theencapsulant 20F. Furthermore, the filler material 26 is shown having anon-uniform distribution over a distance from the surface of theultraviolet device 12 to an external surface of the encapsulant 20F.

FIG. 5 shows an illustrative encapsulant 20G including a plurality oflayers 30A-30C according to an embodiment. In particular, adjacent tothe ultraviolet device 12, the encapsulant 20G can comprise a firstmatrix material 24A with a first filler material 26A embedded therein.Additionally, the encapsulant 20G can comprise a second matrix material24B with a second filler material 26B embedded therein. The encapsulant20G can include a layer 30B of a bonding (e.g., adhesive) material 28,which can adhere the two layers 30A, 30C of composite materials to oneanother. As illustrated, the layer 30C can be shaped as a lens and beattached to the enclosure 14 using the adhesive material 28. It isunderstood that each layer of composite material, such as the layers30A, 30C, can have a composition that is independent of the compositionof the other layer(s). To this extent, the first and second matrixmaterials 24A, 24B and/or the first and second filler materials 26A, 26Bcan comprise the same materials or different materials. Furthermore, thebonding material 28 can comprise the same or a different bondingmaterial as either or both of the matrix materials 24A, 24B.

In an embodiment, the layer 30A can provide a transitional layer fromthe ultraviolet device 12 to the other layers 30B, 30C of theencapsulant 20G. For example, the layer 30A can be formed of an at leastpartially ultraviolet transparent material that is amenable to weldingto a material of the enclosure 14, the ultraviolet device 12, a submount18 (FIG. 1B), and/or the like. In a more particular embodiment, thelayer 30A includes metal alloys, which can be, for example, molybdenum,or the like. Regardless, in an embodiment, a refractive index for eachof the layers 30A-30C can closely match (e.g., within approximately tenpercent of the higher refractive index) a refractive index for theadjacent layer(s).

FIG. 6 shows another illustrative encapsulant 20H including a pluralityof layers 30A-30C according to an embodiment. The encapsulant 20H can beconfigured similar to the encapsulant 20G described herein. However, inencapsulant 20H the particles of the second filler material 26B arearranged to form a plurality of photonic crystals within the outer layer30C of the encapsulant 20G.

The filler material described herein can include multiple types ofmaterials, each of which is included for a particular purpose. Forexample, FIGS. 7A and 7B show illustrative encapsulants 20I, 20J,respectively, including multiple types of filler material according toembodiments. Use of multiple types of filler material can enable, forexample, finer control of refractive and/or physical properties of theencapsulants 20I, 20J. In particular, the encapsulant 20I is shownincluding a first type of filler material 26A and a second type offiller material 26B incorporated in a matrix material 24. The two typesof filler material 26A, 26B can be included for distinct purposes. Forexample, the filler material 26A can comprise fluorescent particles,which visibly fluoresce under exposure to ultraviolet radiation of atarget wavelength, and the filler material 26B can be included tocontrol a thermal coefficient of expansion of the encapsulant 20I. Thefluorescent particles can be selected to identify a wavelength of theultraviolet radiation.

Similarly, the encapsulant 20J is shown including a first type of fillermaterial 26A, a second type of filler material 26B, and a third type offiller material 26C incorporated in a matrix material 24. The threetypes of filler material 26A, 26B can be included for distinct purposes.For example, the filler material 26A can be incorporated to control anindex of refraction of the encapsulant 20J, the filler material 26B canbe included to control a thermal coefficient of expansion of theencapsulant 20J, and the filler material 26C can comprise fluorescentparticles.

While two illustrative combinations of filler materials are shown anddescribed herein, it is understood that an encapsulant can comprise anyof various combinations of two or more filler materials, which areincluded for any purpose. For example, an embodiment of the encapsulant20I can include a combination of two or more filler materials, each ofwhich is selected to allow for better control of both the refractive andthe thermal properties of the encapsulant 20I. In still anotherembodiment, the first filler material 26A can have a first index ofrefraction and the second filler material 26B can have a second index ofrefraction, which is higher or lower than the first index of refraction.A concentration of the fillers within the encapsulant 20I can beconfigured to create a graded index or refraction in the encapsulant20I, e.g., to provide a gradual transition between an index ofrefraction at the surface of the ultraviolet device 12 and an index ofrefraction of the environment surrounding the encapsulant 20I (e.g.,ambient).

While the various filler materials in FIGS. 7A and 7B are shownintermingled throughout the matrix material 24, it is understood thatembodiments of an encapsulant can comprise two or more layersstructures, each with one or more distinct filler materials and/ordistinct matrix materials. For example, FIG. 8 shows an illustrativeencapsulant 20K having a layered structure according to an embodiment.As illustrated, the encapsulant 20K includes a plurality of layers30A-30D. One or more of the layers 30A-30D can be formed of a compositematerial described herein. For example, the layer 30A is formed of acomposite material including a matrix material 24A and a filler material26A, the layer 30C is formed of a composite material including a matrixmaterial 24C and a filler material 26C, and the layer 30D is formed of acomposite material including a matrix material 24D and a filler material26D. However, one or more of the layers, such as the layer 30B cancomprise a unitary layer of material, such as a matrix material 24B,which can include a bonding material, but not include any fillermaterial.

In any event, the various layers 30A-30D can be bonded together by athin layer of a bonding material 28. In an embodiment, the bondingmaterial 28 is a composite material, such as a composite materialdescribed herein. To this extent, similar to the layers 30A, 30C, and30D, the bonding material can be formed of a matrix material and one ormore types of a filler material.

It is understood that a device including an encapsulant described hereincan include one or more additional features to enhance the propagationof ultraviolet radiation through the encapsulant. For example, FIG. 9shows an illustrative device 10C including an anti-reflective coating 32according to an embodiment. The device 10C can include an encapsulant 20comprising a composite material configured as described herein. Theanti-reflective coating 32 can be placed on the outer surface of theencapsulant 20 and can provide a transition between the encapsulant 20and the surrounding environment. In an embodiment, the anti-reflectingcoating 32 comprises a material having a refraction index between arefraction index of the encapsulant 20 and a refraction index of ambientand a thickness selected based on the wavelength of the ultravioletradiation. In an embodiment, the anti-reflective coating 32 comprises athickness of approximately a quarter of a wave of the ultravioletradiation. An index of refraction of the anti-reflective coating 32material can be smaller than an index of refraction of the compositematerial or one or more components thereof (e.g., matrix material,filler material, and/or the like). For example, an index of refractionof the anti-reflective coating 32 can be approximately equal to a squareroot of the index of refraction of the composite material. Illustrativematerials for the anti-reflective coating 32 include magnesium fluoride,fluoropolymers, and/or the like.

FIGS. 10A-10C show illustrative encapsulants 40, 46, 52, respectively,having multiple segments of disjointed domains 42 each forming anoptical element according to embodiments. For clarity, FIGS. 10A-10Conly identify some of the composite domains with reference elements(e.g., 42A, 42B and 42C), however, it is understood that the othernon-identified domains 42 in FIGS. 10A-10C could be represented bysimilar non-overlapping reference elements. As shown in FIGS. 10A-10C,each of the disjointed domains 42 can be separated from an adjacentdisjointed domain by a domain interface 44. For example, as depicted inFIGS. 10A-10C, the disjointed domain 42A can be separated from thedisjointed domain 42B by a domain interface 44. In one embodiment, asshown in FIG. 10A, the domain interfaces 44 can include a gap or airthat separates the domains.

In another embodiment, the domain interfaces 44 can be formed from abonding material that binds the disjointed domains 42 together. Forexample, FIGS. 10B-10C, show that the domain interfaces 44 can include abonding material 45 that binds the disjointed domains 42. In oneembodiment, the bonding material 45 can include a fluoropolymer that isat least partially UV transparent. Such a fluoropolymer can comprisePTFE (e.g., Teflon®), EFEP, and/or the like. In another embodiment, thebonding material 45 can include an encapsulant material used to cover adevice such as any of the previously mentioned materials. For example,as shown in FIGS. 10B-10C, the bonding material 45 or the encapsulantcan be placed at the domain interfaces 44 that separate the disjointeddomains and can extend into an enclosure 48 to provide a protectivepackage covering 50 for an ultraviolet device placed therein.

Although FIGS. 10B-10C do not depict a device, it is understood that adevice such as an ultraviolet device could be packaged with theconfigurations illustrated in these figures such that the encapsulant islocated on an emitting face or underfill of the ultraviolet device,through which ultraviolet radiation of the target wavelength is intendedto pass (into or out of the ultraviolet device) during operation of thedevice. Even though an ultraviolet device is not shown, both of FIGS.10B-10C depict an example of a possible path of a light ray that couldbe generated from an ultraviolet device integrated in the enclosure 48.

The multiple segments of disjointed domains 42 and the domain interfaces44 of the encapsulants 40, 46, 52 of FIGS. 10A-10C can be formed fromone of a number of approaches. For example, a single composite materialthat can be used to form the encapsulants including the disjointeddomains 42 can be cut into a number of different segments. In thismanner, each of the segments of the disjointed domains can form anindividual optical element, such that all of these domains cancollectively form a composite optical element. It is understood that theshapes of the disjointed domains depicted in FIGS. 10A-10C are onlyillustrative of a possible configuration and are not meant to be limitthe various embodiments described herein, as it is well within thepurview of skilled artisans to form domains with varying shapes forcertain applications. Further, it is understood that other approachesbesides cutting can be used to form the multiple segments of disjointeddomains 42 and the domain interfaces 44 of the encapsulants 40, 46, 52of FIGS. 10A-10C. For example, the separate segments can be fabricatedindependently from each other.

The composite optical element that can be formed from each of thesegments of the disjointed domains 42 can include one of a number ofdifferent optical elements. In one embodiment, the composite opticalelement can include a lens. For example, the composite optical elementcan include a lens having at least three disjointed ultraviolettransparent domains. In another embodiment, the composite opticalelement can include a Fresnel lens. Other examples of a compositeoptical element that can be formed from the segments of the disjointeddomains 42 can include, but are not limited to, lenses, mirrors, andlight guiding layers.

The composite material used to form the encapsulants 40, 46, 52 of FIGS.10A-10C, respectively, can include a material that is transparent toultraviolet radiation. For example, the composite material can include,but is not limited to, sapphire, SiO₂, CaF₂, MgF₂, and/or the like. Byforming the segments of the disjointed domains 42 from any of theaforementioned composite materials, these disjointed domains areanalogous to a plurality of composite domains that each form an opticalelement that can collectively be arranged as the composite opticalelement.

In one embodiment, as illustrated in FIG. 10C, at least one of thecomposite domains 54 can be formed from different materials in order toprovide a domain with, for example, different optical properties. Forexample, some of the disjointed domains like domain 54 with differentoptical properties can have different refractive indexes, lightscattering properties, and light transmission characteristics. In oneembodiment, the index of refraction of the domain 54 can differ from theother disjointed domains that also form optical elements by at least 5%.

In one embodiment, these disjointed domains 54 with different opticalproperties can be attained by using different materials. For example, acomposite material containing a filler material such as any of thosepreviously mentioned materials that are at least partially transparentto ultraviolet radiation can be used. For instance, a composite materialthat includes a matrix material at least partially transparent toultraviolet radiation and at least one filler material that is at leastpartially transparent to the ultraviolet radiation incorporated in thematrix material can be used to form a domain with different opticalproperties. In one embodiment, the filler material can include acombination of microparticles and/or nanoparticles such as thosepreviously described in other embodiments.

It is understood that different optical properties can be attainedwithout having some disjointed domains with different materials. Forexample, an encapsulant that can be used as the domain interfaces 44 forbinding the disjointed domains 42 can have an index of refraction thatis different from the index of refraction of the composite materialsused to form the domains 42. In one example, the encapsulant used withthe domain interfaces 44 can include a fluoropolymer with an index ofrefraction that is different from the index of refraction of thecomposite materials used with the disjointed domains 42 that constituteoptical elements. In one example, a fluoropolymer can have an index ofrefraction of 1.3, while the optical elements formed from the disjointeddomains can have an index of refraction of 1.5 or 1.8. In oneembodiment, the index of refraction of the encapsulant used with thedomain interfaces 44 can differ from the disjointed domains that formthe optical elements by no more than 30%.

FIG. 11 shows an illustrative ultraviolet device package 56 having anencapsulant 58 with multiple segments of a disjointed element 60 thatform an optical element according to an embodiment. As shown in FIG. 11,the disjointed element 60 that forms the encapsulant 58 can includemultiple concentric segments 62 that cover an enclosure 64 containing anultraviolet device 12. In one embodiment, the disjointed element 60 canform a Fresnel lens. The Fresnel lens can extend fully across theenclosure opening, or a portion thereof depending on the purpose andfunction of the optical element 60.

In one embodiment, as shown in FIG. 11, portions of some or all of thesegments 62 of the encapsulant 58 can be filled with a material 66 thatenables the encapsulant 58 to attain different optical properties. Forexample, the material 66 can include any one of the aforementionedmaterials that enable different optical properties such as differentrefractive indexes, light scattering properties, and light transmissioncharacteristics.

While shown and described herein as a method of designing and/orfabricating a device package, and particularly a device package for anultraviolet device, it is understood that aspects of the inventionfurther provide various alternative embodiments. For example, in oneembodiment, the invention provides a method of designing and/orfabricating a circuit that includes one or more devices incorporating adevice package designed and fabricated as described herein.

To this extent, FIG. 12 shows an illustrative flow diagram forfabricating a circuit 126 according to an embodiment. Initially, a usercan utilize a device design system 110 to generate a device design 112for a device as described herein. The device design 112 can compriseprogram code, which can be used by a device fabrication system 114 togenerate a set of physical devices 116 according to the features definedby the device design 112. Similarly, the device design 112 can beprovided to a circuit design system 120 (e.g., as an available componentfor use in circuits), which a user can utilize to generate a circuitdesign 122 (e.g., by connecting one or more inputs and outputs tovarious devices included in a circuit). The circuit design 122 cancomprise program code that includes a device designed as describedherein. In any event, the circuit design 122 and/or one or more physicaldevices 116 can be provided to a circuit fabrication system 124, whichcan generate a physical circuit 126 according to the circuit design 122.The physical circuit 126 can include one or more devices 116 designed asdescribed herein.

In another embodiment, the invention provides a device design system 110for designing and/or a device fabrication system 114 for fabricating adevice 116 as described herein. In this case, the system 110, 114 cancomprise a general purpose computing device, which is programmed toimplement a method of designing and/or fabricating the device 116 asdescribed herein. Similarly, an embodiment of the invention provides acircuit design system 120 for designing and/or a circuit fabricationsystem 124 for fabricating a circuit 126 that includes at least onedevice 116 designed and/or fabricated as described herein. In this case,the system 120, 124 can comprise a general purpose computing device,which is programmed to implement a method of designing and/orfabricating the circuit 126 including at least one device 116 asdescribed herein.

In still another embodiment, the invention provides a computer programfixed in at least one computer-readable medium, which when executed,enables a computer system to implement a method of designing and/orfabricating a device as described herein. For example, the computerprogram can enable the device design system 110 to generate the devicedesign 112 as described herein. To this extent, the computer-readablemedium includes program code, which implements some or all of a processdescribed herein when executed by the computer system. It is understoodthat the term “computer-readable medium” comprises one or more of anytype of tangible medium of expression, now known or later developed,from which a stored copy of the program code can be perceived,reproduced, or otherwise communicated by a computing device.

In another embodiment, the invention provides a method of providing acopy of program code, which implements some or all of a processdescribed herein when executed by a computer system. In this case, acomputer system can process a copy of the program code to generate andtransmit, for reception at a second, distinct location, a set of datasignals that has one or more of its characteristics set and/or changedin such a manner as to encode a copy of the program code in the set ofdata signals. Similarly, an embodiment of the invention provides amethod of acquiring a copy of program code that implements some or allof a process described herein, which includes a computer systemreceiving the set of data signals described herein, and translating theset of data signals into a copy of the computer program fixed in atleast one computer-readable medium. In either case, the set of datasignals can be transmitted/received using any type of communicationslink.

In still another embodiment, the invention provides a method ofgenerating a device design system 110 for designing and/or a devicefabrication system 114 for fabricating a device as described herein. Inthis case, a computer system can be obtained (e.g., created, maintained,made available, etc.) and one or more components for performing aprocess described herein can be obtained (e.g., created, purchased,used, modified, etc.) and deployed to the computer system. To thisextent, the deployment can comprise one or more of: (1) installingprogram code on a computing device; (2) adding one or more computingand/or I/O devices to the computer system; (3) incorporating and/ormodifying the computer system to enable it to perform a processdescribed herein; and/or the like.

The foregoing description of various aspects of the invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and obviously, many modifications and variations arepossible. Such modifications and variations that may be apparent to anindividual in the art are included within the scope of the invention asdefined by the accompanying claims.

What is claimed is:
 1. A device package, comprising: an ultravioletdevice for which operation involves ultraviolet radiation of a targetwavelength; and an encapsulant located adjacent to at least one surfaceof the ultraviolet device, wherein the encapsulant is a compositematerial including: a matrix material at least partially transparent toultraviolet radiation of the target wavelength and having a matrixmaterial thermal coefficient of expansion; and at least one fillermaterial at least partially transparent to the ultraviolet radiationincorporated in the matrix material, wherein the at least one fillermaterial includes a combination of microparticles and nanoparticles andhas a filler thermal coefficient of expansion at least three timessmaller than the matrix material thermal coefficient of expansion foratmospheric conditions present during a curing and a cool down processfor fabrication of the device package, and wherein a concentration ofthe at least one filler material in the composite material exceeds apercolation threshold for the filler material.
 2. The device package ofclaim 1, wherein the at least one filler material has a spatialdistribution configured to provide wave guiding for the ultravioletradiation.
 3. The device package of claim 2, wherein the spatialdistribution of the at least one filler material in the encapsulant isradially symmetric with respect to the ultraviolet device.
 4. The devicepackage of claim 1, wherein the at least one filler material has anon-uniform distribution over a distance from the ultraviolet device toan external surface of the encapsulant.
 5. The device package of claim1, wherein the concentration of the at least one filler material variesfrom the at least one surface of the ultraviolet device to an externalsurface of the encapsulant, wherein a refraction index of theencapsulant from the surface of the ultraviolet device to the externalsurface of the encapsulant is graded to gradually transition between arefraction index at the surface of the ultraviolet device to arefraction index of an environment surrounding the external surface ofthe encapsulant.
 6. The device package of claim 1, wherein theultraviolet device is configured to operate as at least one of: anultraviolet light emitting diode, an ultraviolet light emitting laser,an ultraviolet photodetector, an ultraviolet photodiode, an ultravioletphototransistor, an avalanche photodiode, or a photomultiplier.
 7. Adevice package, comprising: an ultraviolet device for which operationinvolves ultraviolet radiation of a target wavelength; an encapsulantlocated adjacent to at least one surface of the ultraviolet device,wherein the encapsulant comprises a plurality of layers, with at leastone of the layers formed of a composite material including: a matrixmaterial at least partially transparent to ultraviolet radiation of thetarget wavelength and having a matrix material thermal coefficient ofexpansion; and a filler material at least partially transparent to theultraviolet radiation incorporated in the matrix material and having afiller material thermal coefficient of expansion at least three timessmaller than the matrix material thermal coefficient of expansion foratmospheric conditions present during a curing and a cool down processfor fabrication of the device package, wherein the filler materialincludes a combination of microparticles and nanoparticles; and atransition layer separating at least two of the plurality of layers ofthe encapsulant, wherein the transition layer includes a bonding layer.8. The device package of claim 7, wherein the filler material includes aplurality of photonic crystals.
 9. The device package of claim 7,wherein each of the plurality of layers of the encapsulant are separatedfrom adjacent layers by a bonding material.
 10. The device package ofclaim 7, wherein the transition layer is substantially unoccupied withany of the filler material.
 11. The device package of claim 7, whereinthe transition layer further includes one of: at least one metal alloyand molybdenum.
 12. The device package of claim 7, wherein the matrixmaterial is interspersed with the microparticles and the nanoparticles.13. A device package, comprising: an ultraviolet device for whichoperation involves ultraviolet radiation of a target wavelength; and anencapsulant located adjacent to at least one surface of the ultravioletdevice, wherein the encapsulant comprises a composite material having aplurality of composite domains shaped to form an optical element locatedabout an emitting surface of the ultraviolet device, each compositedomain having a distinct composition of a matrix material at leastpartially transparent to ultraviolet radiation of the target wavelengthand having a matrix material thermal coefficient of expansion.
 14. Thedevice package of claim 13, wherein each of the plurality of compositedomains comprises an individual optical element.
 15. The device packageof claim 14, wherein plurality of composite domains of individualoptical elements form disjointed ultraviolet transparent domains,wherein each of the disjointed ultraviolet transparent domains areseparated from an adjacent disjointed ultraviolet transparent domain bya domain interface.
 16. The device package of claim 15, wherein each ofthe plurality of composite domains of individual optical elements form alens having at least three disjointed ultraviolet transparent domains.17. The device package of claim 14, wherein at least one compositedomain further includes a filler material at least partially transparentto the ultraviolet radiation incorporated in the matrix material andhaving a filler material thermal coefficient of expansion at least threetimes smaller than the matrix material thermal coefficient of expansion.18. The device package of claim 17, wherein the filler material includesa combination of microparticles and nanoparticles.
 19. The devicepackage of claim 13, wherein the optical element formed from theplurality of composite domains comprises a Fresnel lens.
 20. The devicepackage of claim 13, wherein at least two of the plurality of compositedomains have an index of refraction that differ by at least 5%.